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The cycling mechanism of Li2MnO3 cathode materials synthesized by conventional solid-state methods at high temperatures (800-900 °C) has been intensively investigated. Previous studies showed that CO2 and O2 gas evolution accounts for most of the charge capacity, followed by some Mn reduction during discharge. In this work, we analyze the effects of ball milling on the structure, surface contaminant, and electrochemical capacity of Li2MnO3 cathode material, with or without a graphitic fluoride (C-F) additive. At the same time, C-F is added to form a protective coating layer that reduces unwanted reactions with the electrolyte during later electrochemical cycling. We find that the C-F ball-milled material shows Li2MnO3/LiMnO2 composite phases, while the purely ball-milled material shows a single Li2MnO3 phase. Furthermore, we characterize surface species and gas evolution during the first cycle, which reveals the decomposition of Li2CO3 and the carbonate electrolyte during the first charge, especially during the high potential region (>4.4 V), and the electrochemical reduction of only a small fraction of the evolved gas on the first discharge (

Cost effective modes of transport keeping in conjunction with sustainable outlooks for the future have ensured new technologies and initiatives being taken across the globe. Lighter electric vehicles including two-wheelers or scooters have risen in popularity, with both government and private backed industries investing heavily in green energy. Various state of the art energy systems has been discussed, along with unique approaches to ensure optimum efficiency and lifetime, such as preventing thermal runway reactions, and minimal degradation of electrodes. Supercapacitors, and hybrid fuel cells show potential to be adapted on large scale. New materials and approaches to synthesising​ the former have also been addressed, with emphasis on the powering of the next generation vehicles. Hybrid motor and engine setups developed over the last several years show great improvement and consume minimal quantity of energy. Clever braking technologies further showcase regenerative techniques and improve mileage. Fuel cost comparisons and recycling methodologies are seen to be researched extensively, while multiple challenges have been addressed. Major problems such as reducing carbon footprints and minimising several particulate pollutions present in the atmosphere are demonstrated to be overcome by implementation of electric two wheelers with regions like Europe and Asia showing the most promise in current times. This review will aim to integrate the individual functions and piece the whole system together. Analysis of future opportunities will allow for a comprehensive overview as well.

Coherent nonlinear spectroscopies and imaging in the X-ray domain provide direct insight into the coupled motions of electrons and nuclei with resolution on the electronic length scale and timescale. The experimental realization of such techniques will strongly benefit from access to intense, coherent pairs of femtosecond X-ray pulses. We have observed phase-stable X-ray pulse pairs containing more than 3 × 107 photons at 5.9 keV (2.1 Å) with ∼1 fs duration and 2 to 5 fs separation. The highly directional pulse pairs are manifested by interference fringes in the superfluorescent and seeded stimulated manganese Kα emission induced by an X-ray free-electron laser. The fringes constitute the time-frequency X-ray analog of Young’s double-slit interference, allowing for frequency domain X-ray measurements with attosecond time resolution.

Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications.

Li-S batteries still suffer from two of the major challenges: polysulfide shuttle and low inherent conductivity of sulfur. Here, we report a facile way to develop a bifunctional separator coated with fluorinated multiwalled carbon nanotubes. Mild fluorination does not affect the inherent graphitic structure of carbon nanotubes as shown by transmission electron microscopy. Fluorinated carbon nanotubes show an improved capacity retention by trapping/repelling lithium polysulfides at the cathode, while simultaneously acting as the "second current collector". Moreover, reduced charge-transfer resistance and enhanced electrochemical performance at the cathode-separator interface result in a high gravimetric capacity of around 670 mAh g−1 at 4C. Unique chemical interactions between fluorine and carbon at the separator and the polysulfides, studied using DFT calculations, establish a new direction of utilizing highly electronegative fluorine moieties and absorption-based porous carbons for mitigation of polysulfide shuttle in Li-S batteries. [ABSTRACT FROM AUTHOR]

Alkali and alkaline earth metal-ion batteries are currently among the most efficient electrochemical energy storage devices. However, their stability and safety performance are greatly limited when used with volatile organic liquid electrolytes. A solid state polymer electrolyte is a prospective solution even though poor ionic conductivity at room temperature remains a bottleneck. Here we propose the mixing of two similar polymer matrices, poly(dimethyl siloxane) and poly(ethylene oxide), to address this challenge. The resulting electrolyte matrix is denser and significantly improves room-temperature ionic conductivity. Ab initio analyses of the reaction between the cations and the polymers show that oxygen sites act as entrapment sites for the cations and that ionic conduction likely occurs through hopping between adjacent oxygen sites. Molecular dynamics simulations of the dynamics of both polymers and the dynamics of the polymer mix show that the more frequent and more pronounced molecular vibrations of the polymer mix are likely responsible for reducing the time between two consecutive oxygen entrapments, thereby speeding up the conduction process. This hypothesis is experimentally validated by the practically useful ionic conductivity (σ ≈ 10−4 S cm−1 at 25 °C) and the improved safety parameters exhibited by a transparent flexible multi-cation (Li+, Na+ and Mg2+) conducting solid channel made up of the above mixed polymer system. [ABSTRACT FROM AUTHOR]

Graphite anode have shown commercial success for over two decades, since the start of their use in commercial Li‐ion batteries, due to their high practical specific capacity, conductivity, and low lithiation potential. Graphite is to a large extent thermodynamically unfavorable for sodium‐ion intercalation and thus limits advancement in Na‐ion batteries. In this work, a β‐phase arsenic‐phosphorus monolayer is studied, which has recently been predicted to have semiconducting behavior and to be dynamically stable. First‐principles calculations based on density functional theory are used to explore the role of β‐AsP monolayer as a negative electrode for Na‐ion batteries. Cohesive energy, phonon spectrum, and molecule dynamics simulations confirm the thermodynamic stability and the possibility of experimentally synthesizing this material. The Na‐ion adsorption‐energies are found to be high (>−1.2 eV) on both sides (As‐ and P‐side). The ultra‐fast energy barriers for Na (0.046/0.053 V) over both sides imply high diffusion of Na‐ions on the surfaces of β‐AsP. During the evaluation of Na‐ion anode performance, the fully sodiated state is found to be Na2AsP, which yields a high theoretical‐specific capacity of 506.16 mAh g−1 and low average sodiation potential of 0.43 V versus Na/Na+. [ABSTRACT FROM AUTHOR]

Hybridizing faradaic and non‐faradaic charge storage mechanisms permits hybrid supercapacitors to achieve desirable high energy‐power characteristics. Although the hybridization approach increases the energy density, discrepancies in the reaction kinetics, especially sluggish charge‐transfer reactions in Faradaic battery‐type electrodes, curtails the power density. To increase the power density of battery‐type electrodes, an orthorhombic phase of niobium pentoxide (Nb2O5) is one of the most prominent contenders because the orthorhombic crystal structure provides two‐dimensional transport channels for fast Li‐ion diffusion. However, such ultrafast Li‐ion diffusion cannot be realized due to its electrical‐insulating nature. Herein, we synthesized a composite of the orthorhombic phase of niobium pentoxide (Nb2O5) interconnected with reduced graphene oxide nanosheets via facile microwave assisted methods. Such a dual‐conductive composite anode exhibits excellent rate performance to match that of the cathode which operates conventional adsorption‐desorption charge storage mechanism. By combining the composite anode with a nitrogen doped reduced graphene oxide (N‐rGO) cathode, the device delivers maximum energy density of 89 Wh kg−1 (at 125 W kg−1), and the energy density of 20 Wh kg−1 is retained even at 3500 W kg−1, which is one of the highest energy density reported for Nb2O5 based HSC to the best of our knowledge. Niobium pentaoxide bridging the gap between Li‐ion batteries and Supercapacitors: A high power hybrid supercapacitor comprising of reduced graphene oxide/Nb2O5 nanocomposite cathode and nitrogen doped reduced graphene oxide cathode delivers high energy and power densities. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) chemistry is projected to be one of the most promising for next-generation battery technology, and controlling the inherent "polysulfide shuttle" process has become a key research topic in the field. Regulating intermediary polysulfide dissolution by understanding the metamorphosis is essential for realizing stable and high-energy-density Li-S batteries. As of yet, a clear consensus on the basic surface/interfacial properties of the sulfur electrode has not been achieved, although the catalytic phenomenon has been shown to result in enhanced cell stability. Herein, we present evidence that the polysulfide shuttle in a Li-S battery can be stabilized by using electrocatalytic transition metal dichalcogenides (TMDs). Physicochemical transformations at the electrode/electrolyte interface of atomically thin monolayer/few-layer TMDs were elucidated using a combination of spectroscopic and microscopic analysis techniques. Preferential adsorption of higher order liquid polysulfides and subsequent conversion to lower order solid species in the form of dendrite-like structures on the edge sites of TMDs have been demonstrated. Further, detailed electrochemical properties such as activation energy, exchange current density, rate capabilities, cycle life, etc. have been investigated by synthesizing catalytically active nanostructured TMDs in bulk quantity using a liquid-based shear-exfoliation method. Unveiling a specific capacity of 590 mAh g-1 at 0.5 C rate and stability over 350 cycles clearly indicates yet another promising application of two-dimensional TMDs. [ABSTRACT FROM AUTHOR]

Current lithium ion battery technologies suffer from challenges derived from the eco-toxicity, costliness, and energetic inefficiency of contemporary inorganic materials used in these devices. Small organic molecules containing polycyclic aromatic moieties and polar functional groups have recently been presented as attractive electron donors that bind lithium and other small metal ions. This has endowed them with the potential to replace traditional inorganic electrodes consisting of metal composites. A family of naturally occurring carbonyl compounds, or quinones, have been of particular interest to the scientific community. However, they themselves have been plagued by issues of low voltages, poor conductivity, and capacity fading due to solubility in common polar electrolytes. Herein, we review a number of theoretical and experimental solutions to this problem, which include the use of heterocyclic derivatives, polymers, and conductive supramolecular carbon frameworks as electrochemical property enhancers, or stabilizers, of potential organic electrodes. This review focuses on the benign synthesis, current status, and future direction of organic battery materials with the aim of developing sustainable energy storage systems to meet the demands of a greener future. [ABSTRACT FROM AUTHOR]

Batteries for high temperature applications capable of withstanding over 60 °C are still dominated by primary cells. Conventional rechargeable energy storage technologies which have exceptional performance at ambient temperatures employ volatile electrolytes and soft separators, resulting in catastrophic failure under heat. A composite electrolyte/separator is reported that holds the key to extend the capability of Li-ion batteries to high temperatures. A stoichiometric mixture of hexagonal boron nitride, piperidinium-based ionic liquid, and a lithium salt is formulated, with ionic conductivity reaching 3 mS cm−1, electrochemical stability up to 5 V and extended thermal stability. The composite is used in combination with conventional electrodes and demonstrates to be stable for over 600 cycles at 120 °C, with a total capacity fade of less than 3%. The ease of formulation along with superior thermal and electrochemical stability of this system extends the use of Li-ion chemistries to applications beyond consumer electronics and electric vehicles. [ABSTRACT FROM AUTHOR]

Stabilizing the polysulfide shuttle while ensuring high sulfur loading holds the key to realizing high theoretical energy of lithium--sulfur (Li--S) batteries. Herein, we present an electrocatalysis approach to demonstrate preferential adsorption of a soluble polysulfide species, formed during discharge process, toward the catalyst anchored sites of graphene and their efficient transformation to long-chain polysulfides in the subsequent redox process. Uniform dispersion of catalyst nanoparticles on graphene layers has shown a 40% enhancement in the specific capacity over pristine graphene and stability over 100 cycles with a Coulombic efficiency of 99.3% at a current rate of 0.2 C. Interaction between electrocatalyst and polysulfides has been evaluated by conducting X-ray photoelectron spectroscopy and electron microscopy studies at various electrochemical conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Currently explored Li2MnSnO4/C is a new lithium battery anode material. [•] Li2MnSnO4/C exists in the form of a hybrid with electrochemically active and inactive phases. [•] Carbon triggered and thermally induced reversible formation of Li2MnSnO4 is possible. [•] Newly identified pristine Li2MnSnO4 exists as a single phase compound. [•] Li2SnO3 +Mn2SnO4 +Li2O from Li2MnSnO4/C is responsible for the superior capacity. [Copyright &y& Elsevier]

Highlights: [•] Bi2O3 and In2O3 have been explored for the first time as surface modifiers. [•] Protective metal oxide inter-connect layer reduces irreversible capacity loss. [•] Extended potential window (5.0V) and rate capability (3C) have been realized. [•] Cycling and structural stability up to 100 cycles have been demonstrated. [•] Bi2O3 coated LiNi0.4Mn0.4Co0.2O2 cathode performs better electrochemically. [ABSTRACT FROM AUTHOR]

In this paper, the thermal conductivity behavior of synthetic and natural esters reinforced with 2D nanostructures—single hexagonal boron nitride (h-BN), single molybdenum disulfide (MoS2), and hybrid h-BN/MOS2—were studied and compared to each other. As a basis for the synthesis of nanofluids, three biodegradable insulating lubricants were used: FR3TM and VG-100 were used as natural esters and MIDEL 7131 as a synthetic ester. Two-dimensional nanosheets of h-BN, MoS2, and their hybrid nanofillers (50/50 ratio percent) were incorporated into matrix lubricants without surfactants or additives. Nanofluids were prepared at 0.01, 0.05, 0.10, 0.15, and 0.25 weight percent of filler fraction. The experimental results revealed improvements in thermal conductivity in the range of 20–32% at 323 K with the addition of 2D nanostructures, and a synergistic behavior was observed for the hybrid h-BN/MoS2 nanostructures. [ABSTRACT FROM AUTHOR]

Polymer dielectrics find applications in modern electronic and electrical technologies due to their low density, durability, high dielectric breakdown strength, and design flexibility. However, they are not reliable at high temperatures due to their low mechanical integrity and thermal stability. Herein, a self‐assembled dielectric nanocomposite is reported, which integrates 1D polyaramid nanofibers and 2D boron nitride nanosheets through a vacuum‐assisted layer‐by‐layer infiltration process. The resulting nanocomposite exhibits hierarchical stacking between the 2D nanosheets and 1D nanofibers. Specifically, the 2D nanosheets provide a thermally conductive network while the 1D nanofibers provide mechanical flexibility and robustness through entangled nanofiber–nanosheet morphologies. Experiments and density functional theory show that the nanocomposites through thickness heat transfer processes are nearly identical to that of boron nitride due to synergistic stacking of polyaramid units onto boron nitride nanosheets through van der Waals interactions. The nanocomposite sheets outperform conventional dielectric polymers in terms of mechanical properties (about 4–20‐fold increase of stiffness), light weight (density ≈1.01 g cm−3), dielectric stability over a broad range of temperature (25–200 °C) and frequencies (103–106 Hz), good dielectric breakdown strength (≈292 MV m−1), and excellent thermal management capability (about 5–24 times higher thermal conductivity) such as fast heat dissipation. [ABSTRACT FROM AUTHOR]

Lithium Sulfur (Li/S) chemistries are amongst the most promising next-generation battery technologies due to their high theoretical energy density. However, the detrimental effects of their intermediate byproducts, polysulfides (PS), have to be resolved to realize these theoretical performance limits. Confined approaches on using porous carbons to entrap PS have yielded limited success. In this study, we deviate from the prevalent approach by introducing catalysis concept in Li/S battery configuration. Engineered current collectors were found to be catalytically active towards PS, thereby eliminating the need for carbon matrix and their processing obligatory binders, additives and solvents. We reveal substantial enhancement in electrochemical performance and corroborate our findings using a detailed experimental parametric study involving variation of several kinetic parameters such as surface area, temperature, current rate and concentration of PS. The resultant novel battery configuration delivered a discharge capacity of 700 mAh g−1 with the two dimensional (2D) planar Ni current collectors and an enhancement in the capacity up to 900 mAh g−1 has been realized using the engineered three dimensional (3D) current collectors. The battery capacity has been tested for stability over 100 cycles of charge-discharge. [ABSTRACT FROM AUTHOR]

High theoretical specific capacity and low electrochemical potential offered by lithium metal make it the definitive anode material for lithium batteries. Yet, unrelenting growth of dendrites forestalls the use of Li metal anode in commercial applications. To overcome this issue, we demonstrate the formation of a multi-phase composite protective layer consists of Li x Si alloy, Si-linked organic oligomers and LiCl on the lithium anode surface. Due to its inherent ionic conductivity and chemical stability, the composite film can not only inhibit the formation of lithium dendrites by facilitating uniform Li-ion distribution, but also prevent unfavorable side reactions. The improved electrochemical performance is demonstrated by symmetric cells with the composite layer cycling at 1 mA cm−2 stably for 2200 h. Protected lithium anode coupled with LiFePO 4 achieves high rate performance and better capacity retention after 400 cycles at 1C. Furthermore, cells with protected lithium anode and Li 4 Ti 5 O 12 cathode (high areal loading of 14.9 mg cm−2) shows 91% capacity retention after 400 cycles at 0.5 C. The effective and scalable way to stabilize lithium anode with the multi-phase composite protective layer may serve as good references for development of advanced lithium metal batteries. • A multi-phase composite layer is formed on lithium anode by a scalable method. • The stable composite film efficiently avoids contact between Li and electrolyte. • Uniform Li plating/stripping is realized for the protected Li anode. • The protected Li anode shows much improved electrochemical performance. [ABSTRACT FROM AUTHOR]

In this paper, the thermal conductivity behavior of synthetic and natural esters reinforced with 2D nanostructures-single hexagonal boron nitride (h-BN), single molybdenum disulfide (MoS 2 ), and hybrid h-BN/MOS 2 -were studied and compared to each other. As a basis for the synthesis of nanofluids, three biodegradable insulating lubricants were used: FR3 TM and VG-100 were used as natural esters and MIDEL 7131 as a synthetic ester. Two-dimensional nanosheets of h-BN, MoS 2, and their hybrid nanofillers (50/50 ratio percent) were incorporated into matrix lubricants without surfactants or additives. Nanofluids were prepared at 0.01, 0.05, 0.10, 0.15, and 0.25 weight percent of filler fraction. The experimental results revealed improvements in thermal conductivity in the range of 20-32% at 323 K with the addition of 2D nanostructures, and a synergistic behavior was observed for the hybrid h-BN/MoS 2 nanostructures., Competing Interests: The authors declare no conflict of interest.

Fabrication of lithium-ion batteries that operate from room temperature to elevated temperatures entails development and subsequent identification of electrolytes and electrodes. Room temperature ionic liquids (RTILs) can address the thermal stability issues, but their poor ionic conductivity at room temperature and compatibility with traditional graphite anodes limit their practical application. To address these challenges, we evaluated novel high energy density three-dimensional nano-silicon electrodes paired with 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonyl)imide (Pip) ionic liquid/propylene carbonate (PC)/LiTFSI electrolytes. We observed that addition of PC had no detrimental effects on the thermal stability and flammability of the reported electrolytes, while largely improving the transport properties at lower temperatures. Detailed investigation of the electrochemical properties of silicon half-cells as a function of PC content, temperature, and current rates reveal that capacity increases with PC content and temperature and decreases with increased current rates. For example, addition of 20% PC led to a drastic improvement in capacity as observed for the Si electrodes at 25 °C, with stability over 100 charge/discharge cycles. At 100 °C, the capacity further increases by 3-4 times to 0.52 mA h cm(-2) (2230 mA h g(-1)) with minimal loss during cycling.

Rechargeable batteries capable of operating at high temperatures have significant use in various targeted applications. Expanding the thermal stability of current lithium ion batteries requires replacing the electrolyte and separators with stable alternatives. Since solid-state electrolytes do not have a good electrode interface, we report here the development of a new class of quasi-solid-state electrolytes, which have the structural stability of a solid and the wettability of a liquid. Microflakes of clay particles drenched in a solution of lithiated room temperature ionic liquid forming a quasi-solid system has been demonstrated to have structural stability until 355 °C. With an ionic conductivity of ∼3.35 mS cm(-1), the composite electrolyte has been shown to deliver stable electrochemical performance at 120 °C, and a rechargeable lithium battery with Li4Ti5O12 electrode has been tested to deliver reliable capacity for over several cycles of charge-discharge.